Richard Öchsner’s research while affiliated with Fraunhofer Institute for Integrated Systems and Device Technology and other places

Hydrogen storage in liquid organic hydrogen carriers (LOHC) such as the substance system dibenzyltoluene/perhydro-dibenzyltoluene (H0/H18-DBT) offers a promising alternative to conventional methods. In this contribution, we describe the successful demonstration of the dynamic combined operation of a continuously operated LOHC reactor and a PEM (polymer exchange membrane) fuel cell. The fuel cell was operated stable with fluctuating hydrogen release from dehydrogenation of H18-DBT over a total period of 4.5 h, reaching electrical stack powers of 6.6 kW. The contamination with hydrocarbons contained in the hydrogen after activated carbon filtering did not result in any detectable impairment or degradation of the fuel cell. The proposed pressure control algorithm based on a proportional integral (PI) controller proved to be a robust and easy-to-implement approach to enable the dynamic combined operation of LOHC dehydrogenation and PEM fuel cell.

In order to reduce power peaks in the electrical grid, battery systems are used for peak shaving applications. Under economical constraints, appropriate dimensioning of the batteries is essential. A dimensioning process is introduced consisting of a simulation environment to determine the behavior of the energy system, a real-time peak shaving control algorithm and an optimization process for detection of battery and algorithm parameters. The dimensioning process is investigated on the basis of four exemplary load profiles and in comparison to a conventional approach. Deviations between -7% and 75% for capacity and up to 43% for discharging power indicate undersized batteries using the conventional approach. The proposed approach relies on 1-min measurement data and does not require prediction data, leading to accurate dimensioning results for a given load profile, as verified in simulation. The practical use and effectiveness of the control algorithm is proven in a real-world laboratory. A battery system of 60 kWh capacity and 65 kW maximum power achieved successful peak load reduction by 50 kW (8%) for an a priori defined limit of 570 kW. The comparison with simulation shows only small deviations below 17 kW (4.1%) for the resulting load profile proving the realistic representation of an energy system in simulation.

In this paper, the energy‐saving potential of free cooling in chilled water systems is investigated. As a preliminary study, simulation was used to quantify the performance of free cooling in a given reference system. In order to reduce computational effort for the simulation of long time periods, simplified models for dry and evaporative cooling were developed. The simulation results indicate that free cooling reduces the electric energy demand for cold supply almost by half. In a follow‐up investigation, free cooling was implemented in the reference system. The actual energy‐savings showed good agreements with the simulation forecasts and confirmed the feasibility of the concept.

Hydrogen is used as a carrier gas in the photovoltaics and semiconductor industry. Once scrubbed from poisonous and environmentally harmful substances, the hydrogen-rich waste gas streams are released into the atmosphere. This paper presents an economic analysis of different options for further use of these streams. Combustion in a gas engine with attached electricity generation is currently the most technologically proven and economically profitable solution. With the future rise of the hydrogen electric vehicle infrastructure, power generation via a polymer electrolyte membrane (PEM) fuel cell system could become economically feasible at electricity prices of 0.11 €/kWh and higher. Fuel cells are high tech and modular but still relatively expensive today. Another promising technology identified is the recycling of hydrogen via electrochemical hydrogen compression (EHC). EHC is already economically feasible today at a hydrogen price of 11 €/kg or higher. It will become even more profitable with falling membrane electrode assembly prices.

Industrial facilities usually need multiple energy subsystems, e.g. for heat, cold and electric power supply. Normally those energy subsystems are controlled locally and independent of each other. Coupling of the different subsystems can open up additional potentials. Fraunhofer IISB developed a demonstration and research platform for investigation of the benefits of such sector coupling. A major precondition is to understand the energy flows in the system as well as establishing an overall and flexible system control to realize the required algorithms for setting up an intelligent decentralized energy system. Major components of the overall system are various storages, which extend the degree of freedom for sector coupling as well as increase the effectiveness of the different subsystems.

Commercial polymer electrolyte membrane (PEM) fuel cell systems require pure hydrogen feed gas (ISO 14687-2), otherwise impurities and inert gases would accumulate. Inert gases are difficult to remove, but do not hazard the fuel cell stack itself. Therefore, two purge strategies are introduced and experimentally investigated which enable fuel cell operation with up to 30 vol.% nitrogen content in the feed gas. Both strategies use a commercial on-line hydrogen sensor at the stack outlet either to trigger a discontinuous purge or to control the purge valve continuously. The experimental results show that the discontinuous purge strategy can be applied up to 10 vol.% nitrogen content in the feed gas. The continuous purge strategy was successfully operated with up to 30 vol.% nitrogen content and achieved the theoretical maximum fuel efficiency between 80 and 100%. The influence of nitrogen crossover on fuel efficiency and operating performance was investigated and found negligible. To sum up, the new continuous purge strategy offers an efficient, easy-to-implement, and robust solution to operate polymer electrolyte membrane fuel cell systems with up to 30 vol.% nitrogen content in the feed gas.

In some sectors of industry like coke production, chlorine production or semiconductor manufacturing hydrogen exhaust streams accrue. The hydrogen content can range between 40 – 99 % and represents a huge energy source, which is predominantly not converted into electricity nowadays. A conversion system consisting of a diaphragm compressor, a humidifier and a fuel cell system to convert exhaust gas streams into electricity is presented in this paper. One challenge is to avoid any impact on the process facility and the process itself which is solved by an input pressure control using the compressor and a controlled bypass valve. Furthermore, the influence of nitrogen content in a hydrogen/nitrogen gas mixture on a PEM fuel cell system in flow through mode is investigated on an 8 kW PEMFC. Due to the dilution of hydrogen with up to 60 % nitrogen the maximum output power of the system is dramatically reduced by 55 % to 3.6 kW. The total conversion efficiency depends on exhaust gas conditions, mainly hydrogen concentration and pressure levels, and is expected to be between 10 – 37 %. Another major influence is the fuel cell current density whereby a reduction from 0.5 A/cm2 to 0.2 A/cm2 yields to doubled conversion system efficiency for low hydrogen contents.